Boom angle indicator

ABSTRACT

A boom angle indicator for mobile construction cranes and the like embodies a sending unit mounted directly on the boom pivot shaft and a coacting boom angle display unit in the operator&#39;&#39;s cab. The two units are operatively coupled through a simple pushpull cable with substantially zero play or backlash. The indicator includes means to compensate for a non-level condition of the crane carrier, whereby the indicated boom angle is referenced to the horizontal.

United States Patent Keller, Jr.

1 51 'Feb. 12, 1974 BOOM ANGLE INDICATOR Inventor: Joseph H. Keller, ,lr., Hagerstown,

Assignee: Walter Kidde & Company, Inc.,

Clifton, NJ.

Filed: luly 11, 1972 Appl. No.: 270,671

US. Cl 116/124 F, 212/] Int. Cl. G09f 9/00 Field of Search 116/124 R, 124 F; 212/1;

References Cited UNITED STATES PATENTS 4/1945 Nasset 1 16/124 F 2,941,496 6/1960 Leischer [lb/I24 F Primary Examiner-Louis J Capozi Attorney, Agent, or FirmBrady, OBoyle & Gates 5 7] ABSTRACT A boom angle indicator for mobile construction cranes and the like embodies a sending unit mounted directly on the boom pivot shaft and a coacting boom angle display unit in the operators cab. The two units are operatively coupled through a simple push-pull cable with substantially zero play or backlash. The indicator includes means to compensate for a non-level condition of the crane carrier, whereby the indicated boom angle is referenced to the horizontal.

9 Claims, 6 Drawing Figures- PAIENI FEB) 2 1974 same org BOOM ANGLE INDICATOR BACKGROUND OF THE INVENTION The patented and commercial prior art contains teachings of indicators which give a direct reading of the boom angle on construction cranes and some types of excavating machines. It is essential that some indicating means he provided on telescopic boom cranes, for example, so that a safe loading of the boom can always be determined for a given angle of inclination of the boom and a given degree of boom extension. This indication is required so that the operator may guard against dangerous overloading of the crane which could ultimately result in the equipment tipping over. To be reliable, the boom angle indicator must be highly accurate and the mechanism must be free of backlash and play so that error can be eliminated. At the same time, to be feasible economically, the indicator should be economical to manufacture, install, rugged and durable and should require minimum maintenance.

The prior art devices for this general purpose have generally fallen short of satisfying the above requirements and have tended to be complex and costly and not sufficiently reliable. Some prior art indicators include gearing with inherent build-up of backlash, slotted linkages and springs. These components tend to defeat the purpose of the indicator mechanism for giving an accurate indication of the boom angle where a very small error in indication could prove to be disasterous under the heavy laoding conditions of long crane booms which are encountered in practice. An inaccurate boom angle indicator could be worse than no indicator at all, in the sense that a crane operator would rely upon the faulty indicator and would take conservative action based on experience if no indicator were present.

With the above in mind, the objective of this invention is to provide a very simplified and highly reliable boom angle indicator for cranes and the like which will meet all of the stated requirements and which is economical composed of a minimum number of rugged parts requiring minimum adjustment. The transmission means between the boom angle sending unit and the display or read-out unit is in the simplest possible mechanical form, being a push-pull Bowden transmission cable with essentially no play or backlash. The cable structure is spring-loaded at all times to eliminate backlash. By this means the rotary components of the angle sending and display units are directly connected in a 1:1 ratio driving and driven relationship and the true boom angle will always be visible to the crane operator in the cab. The indicator also features a pendulum-type compensator for any out-of-level condition of the crane carrier whereby the indicated boom angle is automatically referenced to the true horizontal.

Other features and advantages of the invention will become apparent during the course of the following description.

BRIEF DESCRIPTION OF DRAWING FIGURES FIG. 1 is a side elevation of a mobile construction crane equipped with the boom angle indicator embodying the invention.

FIG. 2 is an enlarged fragmentary side elevationof the boom angle sending unit connected directly to the boom pivot shaft;

FIG. 3 is an elevational view of the sending unit taken at right angles to FIG. 2. 1

FIG. 4 is a fragmentary side elevation of the boom angle display unit of the indicator mounted in the operators cab, partly broken away, and on a reduced scale.

FIG. 5 is an elevational view, partly in section, taken at right angles to FIG. 4.

FIG. 6 is a plan view of the display unit, partly in section.

DETAILED DESCRIPTION Referring to the drawings in detail, wherein like numerals designate like parts throughout, the numeral 10 designates a mobile construction crane having an extensible telescopic crane boom 11 mounted on a turntable structure 12 which includes the crane operators cab 13. The entire turntable structure and boom is supported on the usual motorized carrier vehicle 14 which is conventional. The telescopic crane 11 has a main pivot shaft 15 fixed to the base section of the boom and rotatably mounted on a heavy journal block 16 having a separable journal cap 17, this journal structure forming an integral part of the turntable 12.

The boom angle indicator forming the subject matter of the invention embodies a sending unit 18' on the boom pivot shaft and associated turntable structure and a coacting boom angle display unit 19 located in the cab 13 in a position to be conveniently read by the crane operator in the cab 13. The third and final component of the simplified indicator is the push-pull Bowden-type transmission cable 20 through which the units 18 and 19 are operatively connected in a substantially zero backlash driver and driven relationship, to be fully described.

The boom angle sending unit 18 comprises a crank or lever arm 21 which is fixed adjustably to the boom pivot shaft 15 as shown in FIGS. 2 and 3. A channel holder 22 for the lever arm 21 is fixedly secured to one end of the pivot shaft 15 by suitable screws 23. A portion of the lever arm 21 rests slidably in the holder 22 and has a pair of adjustment slots 24 formed therethrough to receive the screws 23. The lever arm 21 extends radially of the boom pivot shaft 15, as indicated. The lever arm 21 may be precisely adjusted radially within the holder 22 by means of the slots 24 and when the screws 23 are tightened, the lever arm of the sending unit is securely locked in the selected adjusted position. This adjustment feature is provided to assure a true 1:1 driving-driven relationship between the sending and display units 18 and 19 of the indicator. The adjustment compensates for any build-up of manufacturing tolerances throughout the parts of the indicator. In some cases, it may be possible to eliminate the adjustment feature for the lever arm 21 without destroying the accuracy and reliability of the indicator.

The unit 18 further embodies a clevis joke 25 pivoted by a clevis pin 26 to the outer end of lever arm 21. One end of a push-pull Bowden cable 27 is conventionally secured to the clevis yoke 25 and is received slidably in a guide casing 28 having a rubber seal 29 at the mouth of the casing in wiping contact with the cable. The semi-rigid cable casing 28 is anchored by a conventional fitting means 30 to a sturdy angle bracket 31, in turn rigidly secured to the adjacent side plate 32 of the crane boom support on the turntable 12.

The boom angle display unit 19 in the operators cab 13 is a narrow and compact assembly, FIG. 5, mounted directly upon the right hand side wall 33 of the cab 13, at a relatively low elevation in the cab so that the crane operator can conveniently look down on the top of the display unit. The unit 19 embodies a mounting plate 34, preferably welded to the cab side wall 33, and carrying a stepped shaft 35 projecting therefrom at right angles thereto near the top of the mounting plate, the stepped shaft being anchored to the mounting plate fixedly by welding or in any other suitable manner.

Rotatably mounted on one intermediate diameter portion of the shaft 35 is the hub or bushing 36 of an arcuate indicator dial 37 having angular scale graduatios 38 visibly provided on its outer face by means of a printed decal or the like. The angular graduations on the indicator dial range from 6 below zero or horizontal to 78 of inclination above horizontal, to thus cover the full range of angular movement of the boom 11 around the axis of its pivot shaft 15. As shown in the drawings, the graduated angle scale is adapted to be read by the crane operator from the top by looking down on the indicator dial 37. The arcuate dial 37 is joined with the rotary bushing 36 through a vertical plate or web 39 integrally connected with both the dial and bushing.

Welded to the web 39 and extending radially of the stepped shaft 35 is a crank or lever arm 40 through which rotary motion is transmitted to the dial 37 by the push-pull cable 27. The lever arm 40 is pivotally connected at its outer end by a clevis pin 41 to a clevis yoke 42 which is secured to the end of the cable 27 remote from the sending unit 18. The end portion of the cable casing 28 adjacent the display unit 19 is anchored by a conventional fitting 43 to an angle bracket 44 fixed rigidly by welding to the mounting plate 34. A tab extension 45 on the angle bracket 44 serves to mount a removable sheet metal cover 46 for the display unit 19, such cover being secured near its lower end to the tab 45 by a screw 47. Near its upper end, the cover 46 is secured as at 48 to a screw-threaded extension 49 on the stepped shaft 35, a spacer ring 50 being intervened between the cover and one shoulder 51 of the stepped shaft.

To remove all backlash or play from the push-pull cable, the cable is maintained spring-loaded at all times. As shown in FIGS. 4 and 5, an expansible coil spring 52 surrounds the relatively stationary cable casing 28 above the mounting bracket 44 and the top end of this spring bears against a washer 53 which is fixedly secured to the cable 27 and adjacent yoke 42. As shown in FIG. 4, the spring 52 also surrounds a rubber seal 54 at the adjacent mouth of the casing 28 similar to the seal 29. The lower end portion of the spring 52 fits snugly over a tapered extension 55 of the fitting means 43 and contacts an annular shoulder 56 on the fitting means for stability, the fitting means being stationary with the bracket 44, as described. Consequently, the spring 52 constantly urges the adjacent end of the cable 27 upwardly and maintains the push-pull cable under tension to eliminate all backlash from the cable transmission means connecting the two units 18 and 19. With this arrangement, plus the fact that the lever arms 21 and 40 are of equal length, any angular movement of the lever arm 21 with the boom pivot shaft 15 will be faithfully transmitted to the display unit lever arm 40 and rotary dial 37 on a direct lzl ratio basis without any lost motion or play. This renders the boom angle indicator direct-acting and extremely accurate and reliable, in addition to the fact that the structure is highly simplified and compact with a minimum number of parts which are rugged and durable.

The display unit 19 further embodies a relatively stationary pointer assembly including a radial pointer arm 57 secured to a hub 58, preferably containing a needle bearing 59 or the like. The hub 58 and needle bearing are mounted on another intermediate step of the shaft 35 adjacent to a shoulder 60 formed by the largest diameter portiob of the stepped shaft. At its leading end, the pointer arm 57 carries a pointer tip 61 overlapping the graduated angle scale on the arcuate dial 37 to facilitate reading the various boom angles. The pointer tip is adjustably connected to the arm 57 by a screw 62 and slot 63 and this adjustment is for the initial zero setting or calibration of the pointer and dial. Once the proper zero setting is obtained, the pointer tip 61 is locked by the screw 62 and further adjustment is not needed thereafter.

The boom angle indicator possesses the additional feature of compensating automatically for any off-level condition of the crane carrier 14. This feature is embodied in a pendulum weight 64 suspended by a rod 65 from the hub 58 of pointer arm 57. The hub 58 has limited rotational movement on the axis of the shaft 35 relative to the dial 37 caused by the compensating action of the pendulum'weight 64. The range of this movement is controlled by a pair of fixed pendulum stops 66 on the mounting plate 34 arranged on opposite sides of the rod 65. This limits the compensating movement of the pointer arm 57 to approximately 5 in either direction relative to horizontal. Therefore, the pointer of the boom angle display unit 19 will always be referenced to the true horizontal even if the crane carrier 14 is in a slightly non-level position.

In view of the foregoing description, the operation of the boom angle indicator should already be clear to anyone skilled in the art. To summarize, any raising or lowering of the boom 11 or change in its angle of inclination will be reflected by rotation of the pivot shaft 15 whih is rigid with the boom base section. Correspondingly, this angular movement will be reflected in an exact movement of the lever arm 21 carried by the pivot shaft 15. When this movement occurs, the springloaded push-pull cable 27 free of any measurable backlash will directly and instantly transmit the identical angular movement to the lever arm 40 of the boom angle display unit 19. Since the lever arms 21 and 40 are of exactly the same length radially from the centers of shafts 15 and 35 to the axes of pins 26 and 41, a true 1:1 transmission of movement through the cable 27 will always occur between the sending unit 18 and the display unit 19. More particularly, this 1:1 ratio of angular movement will exist between the rotary lever arm 21 of the sending unit and the arm 40 of the display unit. Therefore, the dial 37 and pointer of the display unit will always reflect precisely the angle of inclination of the boom 11 with respect to true horizontal, it being understood that the pendulum controlled pointer will enable the device to compensate automatically for any non-level condition of the crane carrier.

The ters and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof but it is recognized that various modifications are possible within the scope of the invention claimed.

I claim:

l. A boom angle indicator for a boom having a pivot shaft connecting the boom for pivotal movement to a support structure, comprising a sending unit, an angle display unit, and a transmission means between said units, said sending unit comprising a radial arm secured directly to the boom pivot shaft about whose axis the boom turns to establish a given angle of inclination for the boom, said display unit comprising a fixed pivot element connected on the support structure, a rotary boom angle indicator means on the fixed pivot element including a radial arm of equal length to the firstnamed radial arm on said sending unit, said transmission means comprising a substantially zero backlash Bowden cable directly interconnecting said radial arms of said sending and display units, and said zero backlash Bowden cable comprising a relatively fixed cable guide casing, a push-pull cable element extending slidably through said guide casing, and a spring connected with the push-pull cable element and serving to tension the latter at all times in one direction to prevent the formation of backlash in said transmission means, whereby an angular movement of the boom will produce identical angular movements of the first and second-named radial arms.

7 2. The structure of claim 1, and means mounting at least one of said radial arms so that the effective radial length thereof may be adjusted.

3. The structure of claim 1, and said spring comprising an expansible coil spring surrounding one terminal end portion of said fixed cable guide casing, one end of the spring bearing on a part of the guide casing and the other end of the spring exerting an axial pressure on said cable element to tension the same.

4. A boom angle indicator for a boom having a pivot shaft connecting the boom for pivotal movement to a support structure, comprising a sending unit, an angle display unit, and a transmission means between said units, said sending unit comprising a radial arm secured directly to the boom pivot shaft about whose axis the boom turns to establish a given angle of inclination for the boom, said display unit comprising a fixed pivot element connected on the support structure, a rotary I boom angle indicator dial on said fixed pivot element having a radial arm of equal length to the first-named radial arm on said sending unit directly secured thereto and turning therewith on the axis of the fixed pivot element, a coacting pointer on the display unit to facilitate reading angle indicia on said dial, and said transmission means comprising a substantially zero backlash Bowden cable directly interconnecting said radial arms of said sending and display units, whereby an angular movement of the boom will produce identical angular movements of the first and second-named radial arms.

5. The structure of claim 4, and said pointer comprising a radial pointer arm having a rotational connection with the fixed pivot element, a pendulum weight extension on said pointer arm and a pair of spaced limit stop elements on said angle display unit engaging said pendulum extension to limit movement thereof with said pointer arm to a few degrees of angular movement, thus enabling said coacting pointer to compensate on the display unit for non-level conditions of a crane carrier mounting a crane boom.

6. The structure of claim 5 and an adjustable pointer tip on said pointer arm enabling said coacting pointer to be initially adjusted accurately to a zero reading on said indicator dial and securely locked in said adjusted position.

7. A boom angle indicator for a boom having a pivot shaft connecting the boom-for pivotal movement to a support structure, comprising a sending unit, an angle display unit, and a transmission means between said units, said sending unit comprising a radial arm secured directly to the boom pivot shaft about whose axis the boom turns to establish a given angle of inclination for the boom, said display unit comprising a mounting plate attachable directly to a fixed structural part of the support structure for the boom, a fixed pivot element connected to said mounting plate and projecting from one side thereof, a rotary boom angle indicator means on the fixed pivot element including a radial arm of equal length to the first-named radial arm on said sending unit, and said transmission means comprising a substantially zero backlash Bowden cable directly interconnecting said radial arms of said sending and display units, whereby an angular movement of the boom will produce identical angular movements of the first and second-named radial arms.

8. The structure of claim 7, and said fixed pivot element being a stepped diameter shaft, said rotary boom angle indicator means comprising a rotary angle indicator dial on one diameter portion of said shaft secured directly to the second-named radial arm, and a coacting pointer having a rotary connection with another diameter portion of said shaft, and means to limit rotary movement of said pointer and secured to said mounting plate.

9. The structure of claim 8 and a cover member for said display unit having a supportive connection with said shaft. 

1. A boom angle indicator for a boom having a pivot shaft connecting the boom for pivotal movement to a support structure, comprising a sending unit, an angle display unit, and a transmission means between said units, said sending unit comprising a radial arm secured directly to the boom pivot shaft about whose axis the boom turns to establish a given angle of inclination for the boom, said display unit comprising a fixed pivot element connected on the support structure, a rotary boom angle indicator means on the fixed pivot element including a radial arm of equal length to the first-named radial arm on said sending unit, said transmission means comprising a substantially zero backlash Bowden cable directly interconnecting said radial arms of said sending and display units, and said zero backlash Bowden cable comprising a relatively fixed cable guide casing, a push-pull cable element extending slidably through said guide casing, and a spring connected with the push-pull cable element and serving to tension the latter at all times in one direction to prevent the formation of backlash in said transmission means, whereby an angular movement of the boom will produce identical angular movements of the first and second-named radial arms.
 2. The structure of claim 1, and means mountIng at least one of said radial arms so that the effective radial length thereof may be adjusted.
 3. The structure of claim 1, and said spring comprising an expansible coil spring surrounding one terminal end portion of said fixed cable guide casing, one end of the spring bearing on a part of the guide casing and the other end of the spring exerting an axial pressure on said cable element to tension the same.
 4. A boom angle indicator for a boom having a pivot shaft connecting the boom for pivotal movement to a support structure, comprising a sending unit, an angle display unit, and a transmission means between said units, said sending unit comprising a radial arm secured directly to the boom pivot shaft about whose axis the boom turns to establish a given angle of inclination for the boom, said display unit comprising a fixed pivot element connected on the support structure, a rotary boom angle indicator dial on said fixed pivot element having a radial arm of equal length to the first-named radial arm on said sending unit directly secured thereto and turning therewith on the axis of the fixed pivot element, a coacting pointer on the display unit to facilitate reading angle indicia on said dial, and said transmission means comprising a substantially zero backlash Bowden cable directly interconnecting said radial arms of said sending and display units, whereby an angular movement of the boom will produce identical angular movements of the first and second-named radial arms.
 5. The structure of claim 4, and said pointer comprising a radial pointer arm having a rotational connection with the fixed pivot element, a pendulum weight extension on said pointer arm and a pair of spaced limit stop elements on said angle display unit engaging said pendulum extension to limit movement thereof with said pointer arm to a few degrees of angular movement, thus enabling said coacting pointer to compensate on the display unit for non-level conditions of a crane carrier mounting a crane boom.
 6. The structure of claim 5 and an adjustable pointer tip on said pointer arm enabling said coacting pointer to be initially adjusted accurately to a zero reading on said indicator dial and securely locked in said adjusted position.
 7. A boom angle indicator for a boom having a pivot shaft connecting the boom for pivotal movement to a support structure, comprising a sending unit, an angle display unit, and a transmission means between said units, said sending unit comprising a radial arm secured directly to the boom pivot shaft about whose axis the boom turns to establish a given angle of inclination for the boom, said display unit comprising a mounting plate attachable directly to a fixed structural part of the support structure for the boom, a fixed pivot element connected to said mounting plate and projecting from one side thereof, a rotary boom angle indicator means on the fixed pivot element including a radial arm of equal length to the first-named radial arm on said sending unit, and said transmission means comprising a substantially zero backlash Bowden cable directly interconnecting said radial arms of said sending and display units, whereby an angular movement of the boom will produce identical angular movements of the first and second-named radial arms.
 8. The structure of claim 7, and said fixed pivot element being a stepped diameter shaft, said rotary boom angle indicator means comprising a rotary angle indicator dial on one diameter portion of said shaft secured directly to the second-named radial arm, and a coacting pointer having a rotary connection with another diameter portion of said shaft, and means to limit rotary movement of said pointer and secured to said mounting plate.
 9. The structure of claim 8 and a cover member for said display unit having a supportive connection with said shaft. 